Isolation And Identification Of Xylaria Sp. L1 From Termite Nursery And Its Biotransformation For Okara

Okara,a by-product of agricultural products processing,is a high-quality biomass resource,but the content of insoluble dietary cellulose such as lignocellulose in okara is high and the comprehensive utilization rate is low.It is the main goal for our study to improve the utilization rate of okara.As an effective means of biorefinery,solid-state fermentation has potential applications of lignocellulosic materials.The termite nest was rich in various kinds of fungus resources.Of these,Xylaria is one of the most important fungus in the abandoned termite nest.Therefore,termite nest is always a high-quality resource for isolating purified lignin-degrading fungi.In this study,a cellulose-degrading strain Xylaria sp.L1 was isolated from an abandoned termite nest,and then its cellulose-degrading ability was analyzed.Furthermore,functional annotation of related genes related to carbohydrate metabolism was performed by De Novo sequencing.At the same time,based on the sequencing analysis results,the effect of solid-state fermentation of okara by the strain was characterized to verify its ability to deal with agricultural products,and the rich polysaccharide after fermentation were further studied.The results were shown as follows,1.Xylaria sp.L1 was successfully isolated and purified from the abandoned termite nest.Combined with morphology and ITS identification,the strain was identified as Xylaria sp.L1.The whole genome sequencing results of the strain showed that size of Raw Data,Clean Data,the assembled genome was 4194 Mb,3233 Mb,36.61 Mb,respectively,including the predicted genes contained 8568 coding genes and 6026 tandem duplicates.Genome functional annotation results showed that there were 1850,5647,6713 and 411 genes in KOG,GO,KEGG and Cazyme databases,and all of which showed a high proportion of carbohydrate metabolism genes.Among them,411 carbohydratemetabolizing enzyme Cazyme genes were annotated to 159 Cazym families,which contained a variety of enzymes related to lignocellulosic degradation.2.The characterization results of okara treated by solid fermentation of the strain showed that during the seven-day treatment,in the early stage,the hyphae growing of the strain gradually filled the substrate space.After 3 days of growth,white mycelium bundles gathered to form large milky white fruiting bodies.Substrate consumption rate accelerated,and the fruiting bodies grew rapidly after 3 days.The main components of okara changed significantly,the crude protein content increased by 30.5%(p < 0.05)and the crude fat content decreased by 55.1%(p < 0.05).The water-soluble crude polysaccharide content reached 28.0%,and the maximum cellulase activity reached 11.37U/g.The cellulose and hemicellulose of the substrate were degraded significantly,and the removal rates were 46.50% and 55.04%(p < 0.05),respectively.The soluble dietary fiber was increased by 47.1%(p < 0.05).FTIR,XRD and SEM showed that the fiber bundles of okara were destroyed,with crystallinity decreasing and porosity increasing significantly during solid-state fermentation.The results indicated that Xylaria sp.L1 strain could effectively improve the proportion of dietary fiber and other substances,and promoted the utilization of okara.3.The substrate polysaccharides after being fermented were determined to be acidic heteropolysaccharides,which were composed of glucuronic acid(63.63%)galacturonic acid(1.65%)glucose(11.88%)arabinose(1.45%)fucose(18.85%).UV and FTIR showed that the purified polysaccharide did not contain protein,nucleic acid and had a uronic acid structure.SEM results showed that the surface of the polysaccharide had a smooth,multi-mesh structure.The rheological results showed that the apparent viscosity of the polysaccharide solution increased by the increase of concentration,decreased by the increase of temperature,and increased under acidic conditions.It was a typical nonNewtonian fluid.Moreover,the results of antioxidant activity indicated that the polysaccharide had the ability to scavenging ABTS,DPPH and hydroxyl radicals.Based on these findings,we combined genome sequencing with solid-state fermentation characterization to investigate the cellulose-degrading ability of Xylaria sp.L1.This study provided a theoretical basis for revealing the degradation of lignocelluloserelated enzyme genes by Xylaria sp.L1 and also provided ideas for the development and application of polysaccharides produced by fungal fermentation in the future.